<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>盒子模型</title>
<link href="style.css" rel="stylesheet" type="text/css">
</head>
<body>
<div id="header"><h1>Header Content</h1></div>
<div id="page">
  <div class="main"><h1>Main Content</h1></div>
  <div class="sidebar"><h1>Sidebar Content</h1></div>
</div>
<div id="footer"><h1>Footer Content</h1></div>  
</body>
</html>